Fire control mechanism for automatic firearms



Dec. 9, 1958 w. R. KUNZ 2,863,359

FIRE CONTROL MECHANISM FOR AUTOMATIC FIREARMS Filed July 25. 1957 2 Sheets-Sheet 1 1"\ g 56" i 7o l2 Ill! 34 46 as 68 V 26 I. I 42 INVENTOR. Willimn ELKLII'IZ BY WZMMQL7T%W w. R. KUNZ 2,863,359

FIRE CONTROL MECHANISM FOR AUTOMATIC FIREARMS Dec. 9, 1958 2 Sheets-Sheet 2 Filed July 25. 1957 as J INVENTOR. WillinmR- Kunz FIRE CON TRUL MECHANHSM F OR AUTOMATIC FIREARMS William R. Kunz, Springfield, Mass, assignor to the United States of America as represented by the Secretary of the Army Application .li'uly 25, 1957, Serial No. 674,264

4 Claims. (Cl. 89-131) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to firearms and more particularly to fire control mechanisms therefor.

It is important that firearms designed for military use be adaptable to as many conditions as possible. There are times that the degree of accuracy desired from a shoulder arm is such that it can only be provided through s ngle fire operation, and there are other times when conditions require maximum fire power produced continuously at a high rate.

I-lowever, when a firearm which is designed to fire at a high rate is operated in short bursts, as is oftentimes required, there is a considerable waste of ammunition as the number of rounds fired through manual control of the firearm trigger is generally in excess of that desired. The general solution of this problem has been to reduce the firing rate of the firearms, which consequently reduces their efliciency, accuracy and the benefits resulting from a cone of fire produced at a high rate.

It is, therefore, the general object of this invention to provide for firearms having a trigger-actuated hammer and a reciprocal bolt, a fire control mechanism whereby a gun may be easily adjusted for continuous fire at the optimum high rate for which it was designed, for single fire, or for short bursts in which a relatively small numlgjr of rounds are dischargedat a high rate of continuous It is another object of this invention to provide a fire control mechanism whereby continuous operation of the firearm is stopped automatically after a predetermined number of discharges, independent of the trigger control.

It is still another object of this invention to provide a fire control mechanism which is rotated through the joint cooperation of the firearm hammer and bolt.

It is a further object of this invention to provide a rotatable fire control mechanism which blocks the movement of the hammer to firing position at predetermined positions to which the fire control mechanism is rotated.

It is a still further object of this invention to provide a fire control mechanism having a pair of concentric sprocket wheels which are rotatably responsive to operation of the firearm through a Geneva movement and which cooperate with a firearm sear, selectively alignable with the sprocket wheels, for blocking movement of the hammer to firing position according to predetermined positions to which said sprocket wheels are rotated.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a partially cross-sectioned side view of the firing mechanism showing the bolt in battery position and the hammer held in cock position by the sear;

Fig. 2 is a view similar to Fig. 1 but showing the bolt in recoil position, the trigger in its rearward position and the hammer in retracted position;

Fig. 3 is a view taken along line 3-3 of Fig. 2;

Fig. 4 is a view similar to Fig. 2 but showing the bolt in battery position and the hammer held in locked position by the cooperation of the selector sear, the Geneva movement and the single-sprocket wheel;

Fig. 5 is a view taken along line 5--5 of Fig. 3; and

Fig. 6 is a perspective view of the firing mechanism showing the parts as positioned in Fig. 4.

Shown in the figures is a firearm receiver 12 in which a bolt 14 is mounted for sliding longitudinal movement responsive to operation of the firearm. Bolt 14 is provided with a reciprocal firing pin 16 which extends therethrough and which is actuatable to fire a chambered cartridge by a firing mechanism 18 contained within receiver 12. Receiver 12 is substantially rectangular in construction and is provided with a left wall 22 and a right wall 24.

Firing mechanism 18 includes a hammer 26 which is pivoted from a firing to a retracted position by bolt 14 during recoil, a bolt actuated automatic sear 28 for releasably holding hammer 26 in the retracted position until the bolt is locked in battery position, a pivotal trigger 30 biased from a retracted to a forward position, a pivotally mounted selector sear 32 which is actuatable by the trigger for releasably holding the hammer in a cocked position after being released from the retracted position and which is movable laterally into selective positions, a Geneva movement 34 and a fire selector device 36 which is integral with said Geneva movement and is cooperable with the selector sear, hammer and bolt for selectively adapting the firearm for continuous fire, single fire or a controlled burst.

Hammer 26 is substantially semicircular in configuration and is pivotally mounted at one end on a transverse pin 38 so that the free end thereof, noted at 40, is engageable with the rear end of firing pin 16 for the actuation thereof when the hammer is in firing position. When hammer 26 is in the firing position, end 40 is positioned vertically above pin 38 and is cammingly engaged by the rear end of bolt 14 so that the hammer is swung rearwardly and downwardly to the retracted position when the bolt first starts to recoil. During the remaining recoil travel of bolt 14, hammer 26 is held in retracted position by the sliding engagement of end 40 with the bottom of the bolt. A spring 42, loaded by hammer 26 during movement to the retracted position, biases the hammer to firing position.

Automatic sear 28 is pivotally mounted at the front end on a pin 44 which is mounted transversely to receiver 12 vertically above pin 38 and is biased in clockwise direction by a spring 46. The rear end of automatic sear 28 is arranged to releasably engage end 40 when hammer 26 is rotated slightly forward from the retracted position. A tang 48 extends rearwardly and downwardly from the rear end of bolt 14 to cooperate with a cam surface 50 on automatic sear 28 to move the automatic sear downwardly to release the hammer when bolt 14 reaches battery position. Tang 48 extends from the rear end of bolt 14 right of the longitudinal center line thereof so as to be movable past hammer 26 without interference therewith and automatic sear 28 is mounted adjacent right wall 24 so as to be engageable by both such tang and end 40 of the hammer.

Selector sear 32 is arcuate in configuration and is pivotally mounted approximately midway the ends thereof on a shaft 52 which is mounted for lateral movement through receiver 12. One end of selector sear 32, noted at 54, extends forwardly for engaging cooperation with hammer 26 and the opposite end, noted at 56, extends upwardly for engaging cooperation with fire selector device 36, as hereinafter described. Selector sear 32 is pivotal between a hammer engaging and a hammer re- Patented Dec. 9, 1958' aaeasse lease-position. Whenselector sear 32 is in the hammer engaging position, forward end 54 is receivable by a catch portion 58 which extends laterally across the outside face of hammer 26 whereby the hammer is releasably held in cocked position. Provided'on shaft S2are three annular recesses 60 which cooperate Wlthfl. spring biased detent 62 for selectively positioning selector sear 32 in'one of three lateral positions while also'being pivotal. Hammer 26 is wide'enough so thatforward end 54 is engageable with catch portion 58 in any of the lateral positions to which selector sear 32 is moved. The ends of shaft 52 project outside of receiver 12 for easy'access by the operator whereby selector sear 32 may be manually movedto any one of the three positions.

Geneva movement 34 includes a'driver portion 64, which extends radially as a flange from the left side of the outer periphery of hammer 26, and a gear wheel 66. The outside perimeter of driver'portion 64 is arcuately formed with pin 38 as a center and is terminated at the forward end, respective to clockwise rotation of hammer 26, by a radial cog portion 68.

Gear wheel 66 is integral with a hub portion 76 rotatably mounted on an axle 72 which extends transversely through receiver12 rearwardly of hammer 26 so as to be engaged by cog portion 65 during movement of hammer 26 from retracted to cock position. Gear wheel 66 is essentially square in configuration with the sides cut concavely according to the radius of the outside periphery of driver portion 64 to" form fourtooth portions 74 at the four corners. Gear wheel 66 is disposed also so that the two tooth portions 74, which are in the uppermost positions, have sliding engagement with the underside of bolt 14 when in recoil position so as to be longitudinally aligned thereby. When the two upper tooth portions 74 are longitudinally aligned, the front one of the two lower tooth portions is in position to be engaged by cog portion 68. Whereby, when bolt 14 is in battery position and hammer 26, is released by trigger 30 to go to firing position, cog portion 68 engages the adjacent one of the tooth portions 74 to rotate gear wheel 66 during initial movement of the hammer. During the remaining movement of hammer 26, the outside periphery of driver portion 64 is received by the adjoining concave side of gear wheel 66 and, as the radii thereof are the same, the rotation of the gear wheel is limited by the engaging cooperation therebetween. As gearwheel 66 is disposed above pin 38, the amount of rotation is less than 90. However, as such rotation is less than 90, the rear one of the upper tooth portions 74 extends upwardly into the path of bolt 14. Therefore, when bolt 14 is recoiled responsive to the firing of the firearm, the one of the tooth portions 74 extending into the path of the bolt is engaged thereby to complete the 90 rotation of gear wheel 66.

Gear wheel 66 is positioned on the left side of hub 70 and fire selector device 36 is spaced therefrom on the right side of such hub. Fire selector device 36 includes a sprocket wheel 78 having four equally-spaced sprockets which are engageable by selector sear 32 to block counterclockwise rotation of the fire selector device and gear wheel 66 when such selector sear-is positioned in the right one of the selected fire positions and is pivoted by trigger 30 to the hammer release position. Fire selector device 36 also includes a single-sprocket wheel 86 which is integral with the inside of one of the sprockets of sprocket wheel 78. Single-sprocket wheel 86 is engageable with selector sear 32 to block counterclockwise rotation of fire selector device 36 and gear wheel 66 when detent 62 is received by the center one of the an nular recesses 60. Single-sprocket wheel 8 is spaced from gear wheel 66 a distance greater than the width of selector sear 32 whereby when the selector sear is moved to the third one of the firing positions, such selector sear when retracted to the hammer release position is away 42. from engagement with fire selector device 36 and is free from interference with gear wheel 66.

Trigger 36 is pivotally mounted on a transverse pin 82 and is provided with an upper portion 86, disposed above pin 82, which is bifurcated longitudinally to receive forward end 54 of selector sear 32. A pin 88 extends transversely through upper portion 86 above forward end 54 whereby when trigger 30 is pulled to the retracted position, such pin engageably rotates selector sear 32 to hammer disengaging position. The bifurcation in upper portion 86 is terminated by end wall 96 which provides the abutment for a spring 92 which acts resiliently against forward end 54 to bias selector sear 32 to the hammer engaging position.

Operation When the firearm is to be operated by sequences of controlled bursts, shaft 52 is manually actuated so that detent 62 is received by the middle one ofthe annular recesses 60. This position is indicated by similarportions of shaft 52 projecting from each side of receiver 12.

With the firearm charged, bolt 14 islocked in battery position and hammer 26 is releasably held in cockedposition by selector sear 32. When trigger 30 is pulled to the retracted position, pin 88 therethrough is moved against forward end 54 of selector sear32 for rotation thereof to release hammer 26. .The released hammer strikes firing pin 16 to ignite the chambered cartridge. The resulting discharge causes bolt 14 torecoil during which hammer 26 is pivoted to retracted position and the rearone of the upwardly disposed tooth portions 74 is engageably moved into longitudinal alignment .with the forward one of such upwardly disposed teeth portions.

With the ensuing counterrecoil of bolt 14, hammer 26 is released therefrom, but is releasably held byautomatic sear 28 until the bolt is locked in battery position whereupon tang 48 actuates such automaticsearthrough the camming engagement with camsurface-Stl, to release the hammer. As selector sear 32 is being held away from engagement with hammer 26 by trigger 30, the hammer pivots from engagement with automatic sear 28 into engagement with firing pin 16 to fire the firearm. During the movement of hammer 26 to firing positio n, cog portion 68 on driver portion 64 engages the forward one of the lowermost tooth portions 74 to; rotate gear wheel 66 until stopped by the engagement of driver portion 64 with the adjacent one of the concave sides of the gear wheel, which is 90 from where such gear'wheel was positioned when the firearm was originally charged.

Firing will continue, as the operator is unable to release trigger 30 fast enough to stop the firing-otherwise,- until single-sprocket wheel is rotated aroundinto engagement with upper end 56 0f selector sear 32 which blocks gear wheel 66 from further rotation. Qonsequently, when hammer 26 is released through the actuation of automatic sear 2% by tang 48, such hammer is prevented from proceeding to firing position by'the engagement of cog portion 68 with the forward one of the-lowermost tooth portions 74.

To produce another burst, trigger 3 0 is released where upon selector sear 32 is free to be rotated by spring 92 to hammer holding position which moves'upper end 56 away from engagement with single-sprocket wheel 80, permitting hammer 26 topivot toward firing position. However, as upper end 56 is rotated away from sprocketfit), forward end 54 is at the same time rotated into position to engage catch portion 58 and so releasably hold the hammer in cocked position. Whereupori, another burst of fire may be produced when trigger 36 is again pulled to retracted position. After the first burst the following bursts will be of four-round duration as gear wheel 66 is rotated during each cycle of operation. The duration of the first burst will depend upon the position of single-sprocket wheel 80 relative to selector sear 32 when the burst is initiated.

To adjust the firearm for single fire operation, shaft 52 is moved so that selector sear 32 aligns with sprocket wheel 78 whereupon hammer 26 is held by one of the four sprockets of such sprocket wheel after each operating cycle with further fire being prevented until trigger 30 is released, as hereinbefore explained for controlled burst firing, and the hammer delivered into engagement with selector sear 32. For continuous automatic fire, selector sear 32 is moved into alignment with the space between gear wheel 66 and fire selector device 36 whereby the operation of the firearm is controlled solely by trigger 30.

From the foregoing it is clearly apparent that there is provided herein an improved fire control mechanism of sturdy construction and positive operation whereby a firearm provided with a hammer device and a reciprocal bolt may be easily adjusted/for single orcontinuous fire operation or for controlled bursts of predetermined duration so that the firearm is adjustable to a wide variety of operating conditions and operatable with an optimum of efficiency and accuracy.

Although a particular embodiment of the invention has been described in detail herein, it is evident that many variations may be devised within the spirit and scope thereof and the following claims are intended to include such variations.

I claim:

1. For automatic firearms provided with a reciprocal bolt and a hammer pivoted from a firing to a retracted position by the bolt during movement from a battery to a recoil position, a fire control mechanism comprising a selector sear for releasably holding the hammer in a cocked position between the retracted and firing positions, a trigger for manually actuating said selector sear to release the hammer, rotary means engageably interposed between said selector sear and the hammer to cooperate with said trigger in releasably blocking movement of the hammer from the retracted to the cocked position to automatically stop operation of the firearm after a predetermined number of rounds have been fired when said selector sear is held by said trigger in a hammer-release position, and means rotated through alternate engagement by the hammer and the bolt for rotating said rotary means one revolution during the firing of such predetermined number of rounds.

2. The device of claim 1 wherein said means for rotating said rotary means comprises a Geneva movement including a gear wheel rotated through alternate engagements by a cooperating driver mounted to the hammer and the bolt.

5 3. For automatic firearms provided with a reciprocal bolt and a hammer pivoted from a firing to a retracted position by the bolt during movement from a battery to a recoil position, a fire control mechanism comprising a selector sear for releasably holding the hammer in a cocked position between the retracted and firing positions thereof, a trigger pivotal from a normal to a retracted position for actuating said sear to a hammer-release position, and a pair of sprocket wheels rotatable one pitch through alternate engagement by the hammer and the bolt therewith and selectively cooperable with said selector sear for releasably blocking movement of the hammer to the firing position according to the number of sprockets on the selected one of said pair of sprocket wheels when said sear is held by said trigger in the hammer-release position.

4. For automatic firearms provided with a reciprocal bolt and a hammer pivoted from a'firing to a retracted position by the bolt during movement from the battery to the recoil position, a fire control mechanism comprising a selector sear for releasably holding the hammer between the retracted and firing position, a trigger pivoted from a normal to a retracted position for actuating said selector sear to release the hammer, a firing selector device, and a Geneva movement for rotating said firing selector device one complete revolution during a predetermined number of operating cycles of the firearm, said Geneva movement including a driver arcuately formed on the hammer, a radial cog portion formed at the leading end of said driver, a gear wheel provided with four equallyspaced tooth portions formed by concave portions having a radius equal to the radius of the outside periphery of said driver and a pin for rotatably mounting said gear wheel respective to said driver and the path of movement of the bolt whereby said gear wheel is rotated during an operating cycle of the firearm through alternate engagement by said driver and the bolt therewith, and said fire selector device including a single-sprocket wheel and a sprocket wheel provided with four sprockets respectively engageable with said selector sear at each firing cycle when said selector sear is held by said trigger in hammerrelease position to block rotation of said gear wheel by said driver and so hold the hammer between the retracted and cocked positions until said trigger is returned to the normal position, and said single-sprocket wheel being disposed for engagement with said selector sear every four cycles of firearm operation to stop operation of the firearm until said trigger is released to the normal position.

References Cited in the file of this patent UNITED STATES PATENTS 

